U.S. patent application number 10/792822 was filed with the patent office on 2004-09-02 for method and apparatus for reproducing data using management data.
This patent application is currently assigned to LG Electronics Inc.. Invention is credited to Kang, Ki Won, Kim, Byung jin, Seo, Kang-soo, Yoo, Jae-Yong.
Application Number | 20040170390 10/792822 |
Document ID | / |
Family ID | 19557791 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040170390 |
Kind Code |
A1 |
Kim, Byung jin ; et
al. |
September 2, 2004 |
Method and apparatus for reproducing data using management data
Abstract
A method and apparatus are provided for creating and recording
management information for digital data streams, and for
reproducing data using the management information. The method for
reproducing data from a recording medium includes receiving an
access time for accessing data from the recording medium, searching
for a target entry point based on the access time by using access
time entries, and searching for a target object unit by using the
target entry point and object unit entries. The access time entries
and the object unit entries are management information stored on
the recording medium.
Inventors: |
Kim, Byung jin; (Kyunggi-do,
KR) ; Seo, Kang-soo; (Kyunggi-do, KR) ; Yoo,
Jae-Yong; (Seoul, KR) ; Kang, Ki Won; (Seoul,
KR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
LG Electronics Inc.
|
Family ID: |
19557791 |
Appl. No.: |
10/792822 |
Filed: |
March 5, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10792822 |
Mar 5, 2004 |
|
|
|
09435362 |
Nov 8, 1999 |
|
|
|
Current U.S.
Class: |
386/241 ;
348/E5.007; 375/E7.004; 386/248; 386/E5.052; 386/E9.013;
G9B/27.012; G9B/27.019; G9B/27.021; G9B/27.033; G9B/27.05 |
Current CPC
Class: |
G11B 27/034 20130101;
H04N 21/8455 20130101; G11B 27/329 20130101; H04N 5/783 20130101;
H04N 5/775 20130101; H04N 9/8042 20130101; G11B 27/3027 20130101;
H04N 21/4334 20130101; H04N 21/4325 20130101; G11B 2220/65
20130101; G11B 27/322 20130101; H04N 21/4135 20130101; H04N
21/440281 20130101; H04N 21/43622 20130101; G11B 27/11 20130101;
H04N 21/43632 20130101; G11B 27/105 20130101; G11B 2220/2562
20130101; H04N 9/8205 20130101 |
Class at
Publication: |
386/095 ;
386/125; 386/126 |
International
Class: |
H04N 005/781 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 1998 |
KR |
98-48097 |
Claims
What is claimed is:
1. A method for reproducing data from a recording medium, the
recording medium containing therein access time entries and object
unit entries associated with object units, the method comprising
the steps of: receiving an access time for accessing data from the
recording medium; searching for a target entry point based on the
access time by using the access time entries; and searching for a
target object unit by using the target entry point and the object
unit entries.
2. The method of claim 1, wherein the access time entries include
index numbers associated with the object units.
3. The method of claim 2, wherein the access time entries further
include location information for the object units.
4. The method of claim 3, wherein the access time entries further
include time duration information identifying a time duration
between two start presentation time positions.
5. The method of claim 1, wherein the object unit entries include
object unit size information and object unit presentation time
information associated with each of the object units.
6. The method of claim 5, wherein the object unit size information
of an object unit identifies a size of that object unit.
7. The method of claim 6, wherein the object unit presentation time
information of an object unit identifies a playing time of that
object unit.
8. The method of claim 4, wherein the object unit entries include
object unit size information and object unit presentation time
information associated with each of the object units.
9. The method of claim 1, wherein the recording medium is a
DVD.
10. An apparatus for reproducing data from a recording medium, the
recording medium containing therein access time entries and object
unit entries associated with object units, the apparatus
comprising: means for receiving an access time for accessing data
from the recording medium; means for searching for a target entry
point based on the access time by using the access time entries;
and means for searching for a target object unit by using the
target entry point and the object unit entries.
11. The apparatus of claim 10, wherein the access time entries
include index numbers associated with the object units.
12. The apparatus of claim 11, wherein the access time entries
further include location information for the object units.
13. The apparatus of claim 12, wherein the access time entries
further include time duration information identifying a time
duration between two start presentation time positions.
14. The apparatus of claim 10, wherein the object unit entries
include object unit size information and object unit presentation
time information associated with each of the object units.
15. The apparatus of claim 14, wherein the object unit size
information of an object unit identifies a size of that object
unit.
16. The apparatus of claim 15, wherein the object unit presentation
time information of an object unit identifies a playing time of
that object unit.
17. The apparatus of claim 13, wherein the object unit entries
include object unit size information and object unit presentation
time information associated with each of the object units.
18. The apparatus of claim 10, wherein the recording medium is a
DVD.
Description
[0001] The present application is a continuation of co-pending U.S.
patent application Ser. No. 09/435,362 filed on Nov. 8, 1999 for
which priority is claimed under 35 U.S.C. .sctn. 120; and the
present application claims priority of Patent Application No.
98-48097 filed in Republic of Korea on Nov. 8, 1998, under 35
U.S.C. .sctn. 119. The entire contents of each of these
applications are herein fully incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method and apparatus for
recording received digital data streams on a recording medium and
creating and recording management information for the recorded
digital data streams. The present invention also relates to a
method and apparatus for reproducing data from a recording medium
using the recorded management information.
[0004] 2. Description of the Related Art
[0005] In conventional analog television broadcast, video signals
are transmitted over the air or through cables after being AM or FM
modulated. With the recent rapid advance of digital technologies
such as digital image compression or digital
modulation/demodulation, standardization for digital television
broadcast is in rapid progress. Based upon the Moving Picture
Experts Group (MPEG) format, satellite and cable broadcast industry
also moves towards digital broadcast.
[0006] Digital broadcast offers several advantages that its analog
counterpart cannot provide. For example, digital broadcast is
capable of providing services with far more improved video/audio
quality, transmitting several different programs within a fixed
bandwidth, and offering enhanced compatibility with digital
communication media or digital storage media.
[0007] In digital broadcast, a plurality of programs encoded based
upon the MPEG format are multiplexed into a transport stream before
transmitted. The transmitted transport stream is received by a set
top box at the receiver and demultiplexed into a plurality of
programs. If a program is chosen from among the demultiplexed
programs, the chosen program is decoded by a decoder in the set top
box and original audio and video signals are retrieved. The
retrieved audio and video signals can be presented by an A/V output
apparatus such as a TV.
[0008] It is also possible to store the received digital broadcast
signals on a storage medium instead of directly outputting the
received broadcast signals to A/V output devices. The stored
digital broadcast signals can be edited and retrieved afterwards.
For example, a digital data stream received by a set top box can be
stored in a streamer such as a digital video disk (DVD) recorder
through communication interfaces like an IEEE-1394 serial bus.
Later, the stored digital data stream can be edited and transmitted
back to the set top box so that the original digital audio and
video data can be presented.
[0009] When a received digital data stream is recorded on a
recording medium, management information regarding the digital data
stream needs to be created and recorded on the recording medium. A
conventional method for creating the management information will
now be explained with reference to FIGS. 1 and 2.
[0010] If a user's request for recording an incoming data stream
tuned by a tuning unit 110 has been received, a control unit 140 of
a set top box 100 informs a control unit 250 of a streamer 200 that
a recording mode is set and begins to transfer the received digital
stream to the streamer 200 through an IEEE-1394 interface. The
control unit 250 of the streamer 200 controls a stream recording
unit 220 to record the received data stream on a recording medium
230. The transport stream packets (TS Pkt 1.about.TS Pkt k)
constituting the data stream are recorded on the recording medium
230 along with respective transport stream packet arrival times (TS
APATs), wherein the transport stream packets with packet, arrival
times are organized in sectors on the recording medium 230.
[0011] When recording the digital stream, the control unit 250 of
the streamer 200 groups the transport stream packets into stream
object units (SOBU 1.about.SOBU q), with each stream object unit
(SOBU) having a predetermined time length, for example, 0.5 s. The
control unit 250 also creates a stream object unit size (SOBU_SZ)
and a stream object unit presentation time (SOBU_TM) for each
stream object unit (SOBU) and records the created information as
management information for the associated stream object unit
(SOBU). The stream object unit size (SOBU_SZ) of a stream object
unit (SOBU) is expressed in terms of the number of sectors
containing the stream object unit. If 20 stream object units
(SOBUs) are created after 10 s elapses, the control unit 250
creates and records a stream object unit index number (SOBU_N) for
the 20 stream object units.
[0012] The control unit 250 of the streamer 200 conducts the
aforementioned task until the recording mode terminates, thereby
creating a record (RCD) or program (PG). The digital stream
recorded by a single recording operation is called a record (RCD)
or program (PG). After the recording mode ends, the control unit
250 of the streamer 200 groups the created stream object units
(SOBUs) into a stream object (SOB) and groups stream object unit
sizes (SOBU_SZs) into a map. The map is recorded on the recording
medium 230 as stream object information (SOBI).
[0013] Subsequently, the control unit 250 of the streamer 200
creates and records a presentation sequence information (Cell) with
information linking it to the corresponding record (RCD) or program
(PG).
[0014] If a user enters a search time (HH:MM:SS:FF) in order to
search for a specific position on the recording medium 230, the
control unit 250 of the streamer 200 detects a record (RCD) or
program (PG) corresponding to the user's search time (HH:MM:SS:FF)
with reference to the creation times (PG1_Create_TM, PG2_Create_TM,
PG3_Create_TM) of records (RCD1.about.RCD3) or programs
(PG1.about.PG3). Suppose the detected program is PG2 shown in FIG.
2. Then, the control unit 250 detects a Cell (Cell 2 shown in FIG.
2) corresponding to the user's search time (HH:MM:SS:FF) with
reference to the presentation start time (C1_S_TM, C2_S_TM, . . . ,
Cn_S_TM) and presentation end time (C1_E_TM, C2_E_TM, . . . ,
Cn_E_TM) of each Cell contained in the detected program PG2.
[0015] Referring to the stream object information (SOBI) of the
stream object SOB2 associated with the detected presentation
sequence information Cell 2, the control unit 250 subtracts the
stream object start time (SOB_S_TM) from the user's search time
(HH:MM:SS:FF) The control unit 250 searches for a stream object
unit (SOBU) based upon the size accumulated up to the stream object
unit (SOBU) in which the presentation time accumulated up to the
stream object unit (SOBU) is closest to the subtraction result
without exceeding it.
[0016] Suppose that the stream object unit detected by the
above-mentioned procedure is SOBUg shown in FIG. 2. As the next
step, the control unit 250 detects the transport stream packet
arrival time (TS APAT) of each transport stream packet from the
first sector Sector 1 containing the detected stream object unit
SOBUg and compares the packet arrival time with the user's search
time (HH:MM:SS:FF). The control unit 250 starts to retrieve
recorded data from the transport stream packet whose packet arrival
time is after the user's search time and controls a stream
reproducing unit 240 so that the retrieved data can be transferred
to the set top box 100 through the IEEE-1394 interface 210.
[0017] As explained thus far, each stream object unit created by
the conventional data stream recording method has a predetermined
time length. Therefore, in the instance where the transport stream
packet corresponding to the user's search time is the last
transport stream packet recorded in the last sector (Sector n) of
the associated stream object unit (SOBUg) as shown in FIG. 3, a
significant search time is required to locate the target transport
stream packet. This is because it takes time to obtain the packet
arrival time of the last transport stream packet recorded in the
last sector (Sector n) since the packet arrival time of the first
transport stream packet recorded in the first sector (Sector 1) has
been detected.
[0018] The required search time can be fairly reduced by decreasing
the time length of each stream object unit. In this case, however,
the number of stream object units (SOBUs) increases, which
inevitably entails increased amount of overall navigation data as
the management data regarding stream object units also
increases.
[0019] In addition, since the time length of each stream object
unit is fixed, the size of each stream object unit depends on the
bit rate of the input data stream. For example, if an input digital
data stream has a bit rate of 10 Mbps, the size of a stream object
unit (SOBU) amounts to about 5 Mbit and thus the maximum search
time required for locating a transport stream packet within a
stream object unit (SOBU) is about 500 ms. In contrast, in the case
of a data stream with a bit rate of 0.5 Mbps, a stream object unit
(SOBU) has a size of 500 Kbit and the maximum search time required
for locating a transport stream packet within a stream object unit
(SOBU) amounts to about 50 ms.
[0020] Unless every recorded program or record has the same
transfer rate, the size of a stream object unit varies depending on
the transfer rate as shown in FIG. 4. The maximum search time,
therefore, increases in proportion to the size of a stream object
unit and transfer rate. Consequently, the search time is dependent
upon the transfer rates of data streams in the conventional method,
which may result in confusions and problems.
SUMMARY OF THE INVENTION
[0021] It is an object of the present invention to provide a method
and apparatus for creating and recording management information for
digital data streams. When recording a received digital transport
stream on a recording medium, stream object units are created so
that the maximum search time required for locating a specific
position within a stream object unit is uniform among recorded
stream object units.
[0022] It is another object of the present invention to provide a
method and apparatus for reproducing data from a recording medium
using management information stored on the recording medium.
[0023] It is another object of the present invention to provide a
method and apparatus for reproducing data from a recording medium,
which overcome the limitations and disadvantages related to
conventional reproducing methods and apparatuses.
[0024] According to one aspect, the present invention provides a
method for reproducing data from a recording medium, the recording
medium containing therein access time entries and object unit
entries associated with object units, the method comprising the
steps of: receiving an access time for accessing data from the
recording medium; searching for a target entry point based on the
access time by using the access time entries; and searching for a
target object unit by using the target entry point and the object
unit entries.
[0025] According to one aspect, the present invention provides an
apparatus for reproducing data from a recording medium, the
recording medium containing therein access time entries and object
unit entries associated with object units, the apparatus comprising
a combination of elements for receiving an access time for
accessing data from the recording medium, for searching for a
target entry point based on the access time by using the access
time entries, and for searching for a target object unit by using
the target entry point and the object unit entries.
[0026] These and other objects of the present application will
become more readily apparent from the detailed description given
hereinafter. However, it should be understood that the detailed
description and specific examples, while indicating preferred
embodiments of the invention, are given by way of illustration
only, since various changes and modifications within the spirit and
scope of the invention will become apparent to those skilled in the
art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate the preferred
embodiments of the invention, and together with the description,
serve to explain the principles of the present invention.
[0028] In the drawings:
[0029] FIG. 1 is a block diagram of an apparatus in which the
present invention can be advantageously employed;
[0030] FIG. 2 is a pictorial representation showing the syntax of
the recorded data and the management information regarding the
recorded data for explaining a conventional method for creating
management information for data streams recorded on a recording
medium and searching for recorded data using the management
information;
[0031] FIG. 3 is a pictorial representation for explaining the
problems of the conventional method shown in FIG. 2;
[0032] FIG. 4 is a pictorial representation showing the size of a
stream object unit created by the conventional method;
[0033] FIG. 5 is a pictorial representation showing the syntax of
the recorded data and the management information regarding the
recorded data created by the present invention; and
[0034] FIG. 6 is a pictorial representation showing the size of a
stream object unit created by the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] In order that the invention may be fully understood,
preferred embodiments thereof will now be described with reference
to the accompanying drawings.
[0036] FIG. 1 depicts a block diagram of an apparatus in which the
present invention may be advantageously employed. The apparatus
comprises a set top box 100, a communication interface (IEEE-1394),
and a streamer 200, all operatively coupled.
[0037] The set top box 100 receives transport streams encoded by
system encoders and broadcast by a plurality of broadcast stations
and demultiplexes the received transport streams. After a decoder
120 decodes the transport stream of a program tuned by a tuning
unit 110, a control unit 140 outputs the decoded transport stream
to an A/V output apparatus or to the streamer 200 through the
IEEE-1394 communication interface for recording the transport
stream.
[0038] In the set top box 100, the program service information (SI)
contained in the transport stream of the program tuned by the
tuning unit 110 is decoded by the decoder 120 and transmitted to
the control unit 140. The control unit 140 stores the program
service information (SI) in the program information area (M1) of a
memory 150. The program service information (SI) includes
information on all programs of every received channel, such as
channel numbers, channel names, program names, schedules, program
categories, attributes of streams constituting each program,
etc.
[0039] The control unit 140 may constitute a program table having a
time axis and a channel axis using the program service information
(SI) stored in the program information area M1 of the memory 150
and display the program table on a television screen.
[0040] The set top box 100 may transmit a program chosen by a user
through the IEEE-1394 interface to the streamer 200 so that the
transmitted program is recorded on a recording medium 230 such as a
digital video disk (DVD) by the streamer 200.
[0041] In addition, requested by a user, the set top box 100 may
receive a program retrieved from the recording medium 230 by the
streamer 200 through the IEEE-1394 communication interface so that
the received program can be presented on a television after being
decoded by the decoder 120.
[0042] The method for creating and recording management information
for a digital data stream in accordance with an embodiment of the
present invention will now be explained with reference to FIGS. 1
and 5.
[0043] If a user's request for recording an incoming data stream
tuned by the tuning unit 110 shown in FIG. 1 has been received, the
control unit 140 of the set top box 100 informs a control unit 250
of the streamer 200 that a recording mode is set and begins to
transfer the received digital stream to the streamer 200 through an
IEEE-1394 interface. The control unit 140 of the set top box 100
detects the bit transfer rate of the received data stream and
transfers the detected bit transfer rate to the streamer 200,
wherein the bit transfer rate can be obtained by detecting the
elementary stream rate (ES rate) contained in the header of each
packetized elementary stream packet (PES packet) or the piecewise
rate (PW rate) contained in the header of each transport stream
packet.
[0044] The control unit 250 of the streamer 200 controls a stream
recording unit 220 so that the data stream received through the
IEEE-1394 interface can be recorded on the recording medium 230.
The transport stream packets (TS pkt 1.about.TS pkt k) constituting
the data stream are organized in sectors (Sector 1.about.Sector n)
on the recording medium 230 along with respective packet arrival
times expressed in terms of internal clock values. The control unit
250 of the streamer 200 varies the time length of a stream object
unit (SOBU) depending upon the bit transfer rate of the received
data stream transmitted by the set top box 100.
[0045] First, the minimum time length of a stream object unit
(SOBU), the upper threshold value of the transfer rate
(Upper_Th_Rate), and the lower threshold value of the transfer rate
(Lower_Th_Rate) are determined. Suppose that the minimum time
length, the upper threshold value, and the lower threshold value
are set to 0.1 s, 7 Mbps, and 4 Mbps, respectively. If the transfer
rate of a data stream (S_RATE) is equal to or greater than the
upper threshold rate (Upper_Th_Rate), the data stream is classified
into Type 1 and the minimum time length 0.1 s is assigned as the
time length of a stream object unit (SOBU) associated with the data
stream. If the transfer rate of a data stream (S_RATE) is less than
upper threshold rate (Upper_Th_Rate) but greater than the lower
threshold rate (Lower_Th_Rate), the data stream is classified into
Type 2. The stream object unit (SOBU) associated with the data
streams belonging to Type 2 has a time length of 0.2 s which is the
minimum time length 0.1 s multiplied by a predetermined weighting
factor 2. Data streams which do not belong to either Type 1 or Type
2 are classified into Type 3 and the stream object unit (SOBU)
associated with data streams of Type 3 has a time length of 0.3 s
which is the minimum time length 0.1 s multiplied by a
predetermined weighting factor 3. It is desirable to record the
time length of a stream object unit (SOBU) in the stream object
information (SOBI) area because the transfer rate of a program
remains unchanged and therefore every stream object unit (SOBU)
belonging to a stream object (SOB) has the same time length.
[0046] The minimum time length of a stream object unit (SOBU) 0.1
s, the upper threshold rate 7 Mbps, the lower threshold rate 4
Mbps, and the weighting values 2 and 3 mentioned before are simply
illustrative values and thus can be set differently. Likewise, it
is also possible to increase or decrease the number of data stream
groups and assign an appropriate weighting factor to each data
stream group though digital data streams are classified into three
groups depending on their transfer rates in the previous
example.
[0047] With reference to the time information contained in the
transport stream packet such as the program clock reference (PCR),
packet arrival time (PAT), or presentation time stamp (PTS), the
control unit 250 of the streamer 200 records the received data
stream as a series of stream object units (SOBU 1.about.SOBU q),
each stream object unit having a time length determined by the
transfer rate of the received data stream. In addition, the stream
object unit size (SOBU_SZ) of a stream object unit expressed in
terms of the number of sectors containing the stream object unit is
created. As a result, the stream object unit size (SOBU_SZ) and the
stream object unit presentation time (SOBU_TM) for each SOBU, which
are also referred to herein as object unit entries, are recorded on
the medium 230 as management information of the stream object units
(SOBUs). If a predetermined number, for example 20, of stream
object units are created while repeating the above task, the
control unit 250 creates and records access time entries which
include a stream object unit index number (SOBU_N), an accumulated
presentation time (ACC_TM), and an accumulated size (ACC_SZ) for
the 20 stream object units. The accumulated presentation time
(ACC_TM) and accumulated size (ACC_SZ) for each of 20 stream object
units are the presentation time and size accumulated from the start
position (SOB#n_OFF_ADDR) of the stream object (SOB#n) containing
the associated stream object units to each of 20 stream object
units, respectively.
[0048] The control unit 250 of the streamer 200 performs the
aforementioned operation until the recording mode terminates,
thereby creating a record (RCD) or program (PG). After the
recording mode ends, the control unit 250 of the streamer 200
groups the recorded stream object units (SOBUs) into a stream
object (SOB) and groups the recorded accumulated sizes (ACC_SZs),
the recorded accumulated presentation times (ACC_TMs) and the
created stream object unit sizes (SOBU_SZs) into a map. The map is
recorded as stream object information (SOBI).
[0049] Subsequently, the control unit 250 of the streamer 200
creates a presentation sequence information (Cell) for the map and
records it as the cell information corresponding to the record or
program.
[0050] Let us consider the size of a stream object unit (SOBU)
recorded by the embodiment of the present invention. Suppose that
as shown in FIG. 6 the programs PG 1, PG 2, PG 3, and PG4 have
transfer rates of 6 Mbps, 3 Mbps, 4 Mbps, and 6 Mbps, respectively.
Also, suppose that the weighting factors are set to 1.5 and 2 and
the upper threshold rate (Upper_Th_Rate) and lower threshold rate
(Lower_Th_Rate) are set to 6 Mbps and 3 Mbps, respectively.
[0051] Since the transfer rate (S_RATE) of the program PG 1 or RCD
1 is equal to the upper threshold rate 6 Mbps, the program PG1 is
classified into Type 1. Assume that the time length of each stream
object unit (SOBU) of the program PG 1 is set to P s and the size
of each stream object unit (SOBU) amounts to S Mbit. Since the
transfer rate (S_RATE) of the program PG 2 or RCD 2 is equal to the
lower threshold rate 3 Mbps, the program PG 2 is classified into
Type 3. In this case, the time length of each stream object unit
(SOBU) of the program PG 2 is 2 P s and the size of each stream
object unit is S Mbit. Likewise, the program PG 3 is classified
into Type 2. Therefore, the time length of each stream object unit
(SOBU) of the program PG 3 is 1.5 P s and the size of each stream
object unit is S Mbit.
[0052] As seen from FIG. 6, the size of each stream object unit
(SOBU) remains identical without regard to the transfer rates of
input data streams, thereby guaranteeing the maximum search time
required for locating a transport stream packet within a stream
object unit (SOBU) to be uniform.
[0053] If a user enters a search time (HH:MM:SS:FF) in order to
search for a specific position on the recording medium 230, the
control unit 250 of the streamer 200 detects a record (RCD) or
program (PG) corresponding to the user's search time (HH:MM:SS:FF)
with reference to the creation times (PG1_Create_TM, PG2_Create_TM,
PG3_Creat_TM) of records (RCD1.about.RCD3) or programs
(PG1.about.PG3) . Suppose the detected program is PG2 shown in FIG.
5. Then, the control unit 250 detects a Cell (Cell 2 shown in FIG.
5) corresponding to the user's search time (HH:MM:SS:FF) with
reference to the presentation start time (C1_S_TM, C2_S_TM, . . . ,
Cn_S_TM) and presentation end time (C1_E_TM, C2_E_TM, . . . ,
Cn_E_TM) of each Cell contained in the detected program PG2. After
obtaining the time length of a stream object unit (SOBU) from the
stream object information (SOBI) concerning the stream object SOB 2
associated with the detected cell Cell 2, the control unit 250
multiplies the stream object unit index number (SOBU_N) by the
obtained time length. The control unit 250 searches for an
accumulated entry (ACC Entry: the entry to access, which is
gray-marked in FIG. 5) containing the stream object index number
(SOBU_N) in which the multiplication result is closest to the
difference between the user's search time (HH:MM:SS:FF) and the
stream object start time (SOB_S_TM) without exceeding it. Next, the
control unit 250 searches for a target stream object unit (SOBU)
containing the user's search time by multiplying the time length of
a stream object by the number of stream object units counted from
the stream object unit pointed to by the detected accumulated entry
(ACC Entry). The position of the target stream object unit (SOBU)
can be obtained by adding the accumulated size (ACC_SZ) of the
target accumulated entry (ACC Entry) to the sum of stream object
sizes (SOBU_SZs) calculated from the stream object unit pointed to
by the target accumulated entry (ACC Entry).
[0054] Suppose that the stream object unit detected by the
above-mentioned procedure is SOBUg shown in FIG. 5. As the next
step, the control unit 250 detects the transport stream packet
arrival time (TS APAT) of each transport stream packet from the
first sector Sector 1 containing the detected stream object unit
SOBUg and compares the packet arrival time with the user's search
time (HH:MM:SS:FF). The control unit 250 starts to retrieve
recorded data from the transport stream packet whose packet arrival
time is after the user's search time and controls a stream
reproducing unit 240 so that the retrieved data can be transferred
to the set top box 100 through the IEEE-1394 interface 210.
[0055] The invention may be embodied in other specific forms. For
example, the invention is not only applicable to the apparatus
shown in FIG. 1 but applicable to any system comprising a subsystem
functioning as a set top box, another subsystem functioning as
streamer, and a communication interface between the two
systems.
[0056] In the previous embodiment, the set top box detected the bit
rate of a data stream and transmits the detected value to the
streamer. It is also possible, however, for the streamer to
calculate the bit rate by detecting the elementary stream rate (ES
rate) contained in the header of each packetized elementary stream
packet (PES packet) or the piecewise rate (PW rate) contained in
the header of each transport stream packet after scrambling and
decoding the input data stream.
[0057] Instead of calculating the bit rate of a data stream from
the ES rate or PW rate, the data transfer rate information such as
the ES rate or PW rate can be used directly. Also, the bit rate can
be calculated from the amount of data between two consecutive
program clock references (PCRs) contained in the data stream,
wherein the bit rate is given as [the data amount (in
bytes).times.system clock frequency]/[PCR j-PCR i].
[0058] In the previous embodiment, it was assumed that the bit rate
of a program remained unchanged throughout the program. The present
invention is still applicable to data streams in which the upper
and lower limits of the bit rate of the data stream are given.
[0059] The invention may be embodied in other specific forms
without departing from the sprit or essential characteristics
thereof. The present embodiments are therefore to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description and all changes which come within the meaning
and range of equivalency of the claims are therefore intended to be
embraced therein.
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